The aim of the proposed research is to determine whether an individual has acquired an adult reading vocabulary and to develop an effectiveness measure of growth towards adult vocabulary literacy. The adult corpus is defined in terms of the difficulty of informational materials written for a general adult audience. Grade-level corpora are defined in terms of the difficulties of series textbooks designated for each grade. all these corpora were identified during Phase I, when the largest (over 16,000,000 tokens) systematic word frequency count ever done was conducted. Vocabulary measures will be developed in Phase II by drawing stratified samples from the frequency bands of the adult corpus and testing for lexical meanings. Latent trait models and TASA's calibration designs will be used to obtain sample free estimates of vocabulary item difficulty. Phase II research should show that several factors account for difficulty of vocabulary test items including the frequency of the word selected in the adult corpus, the relative frequency of the work in corpora that form the developmental scale, and the relative frequency of the word's lexical meaning. Semantic analyses conducted for test development will form the basis for semantic word counts.